FOREWORD: A USER'S GUIDE TO THE MANUAL
SECTION I: THE ECOLOGY OF TROPICAL TREES AND FORESTS:
A CRASH COURSE
Tree Density and Abundance
Flowering, Fruiting, and Reproductive
Dynamics
Phenology of Flowering
and Fruiting
Pollination
Seed Dispersal
Regeneration and Growth
Canopy Gaps
Regeneration Guilds
Population Structure
Literature
SECTION II: IMPACT OF HARVESTING
Fruits and Seeds
Plant Exudates
Vegetative Structures
Literature
SECTION III: SIX STEPS TO SUSTAINABILITY
Species Selection
Forest Inventory
Yield Studies
Regeneration Surveys
Harvest Assessments
Harvest Adjustments
A Note About Remedial Treatment
Literature
One of the most basic and rarely questions assumptions underlying much of the current interest in non-timber tropical forest resources is that the commercial harvesting of these commodities has little or no impact on a tropical forest. This ubiquitous idea has appeared in books, magazines, and newspapers, on television and radio shows...and even on the back of ice cream cartons. Unfortunately, this assumption is both untenable and potentially dangerous.
If intensive resource extraction is the only activity planned within a tropical forest, there is a very high probability that these resources will be gradually depleted over time. The basic tenets of forest ecology tell us this. So does the long history of forest exploitation in the tropics. Regardless of the species, land tenure, or marketing system involved, collectors simply cannot harvest commercial quantities of fruits, nuts, latexes, and oil seeds year after year and then expect the forest to magically replenish these stocks. As elsewhere, there is no free lunch in a tropical forest.
In reality, the sustainable harvest of non-timber tropical forest resources requires quite a bit more than "blind faith" in the productive capacity of tropical plants. It requires careful selection of species, resources and sites. It requires controlled harvesting and periodic monitoring of the regeneration and growth of the species being exploited. More than anything, however, it requires a greater appreciation of the fact that ecology and forest management are the cornerstones of sustainable resource exploitation. There are ways to harvest non-timber products without damaging a tropical forest. This report will hopefully provide a framework for taking the first steps to achieve such an objective.
OBJECTIVES
The main objective of this report is to give a concise overview of the ecology
and exploitation of non-timber tropical forest resources in terms that can be
easily understood by non-specialists. The material has been written with two
potential audiences in mind. In the first group are the innumerable NGOs, individual
entrepreneurs, "green" businesses, and other commercial concerns who are currently
promoting the increased exploitation of non-timber tropical forest products.
The second group includes local community organizations, extension agents and
forest managers who are already actively involved in the harvest of these resources.
Although the setting, frame of reference, and scale of operations may be different
in each case, both groups have a vested interest in the long-term sustainability
of tropical forest exploitation.
The controlled exploitation of non-timber forest products holds great potential as a method for integrating the use and conservation of tropical forests. This report attempts to narrow the gap between the potential and the reality of this land-use practice. The following pages provide a general background on the ecology of non-timber resources and present a series of management operations designed to minimize the impact of harvesting these resources. The procedures described are not a blueprint for eliminating the potential impacts on all components of a forest ecosystem (e.g. soils, hydrology, or associated plant and animal species), or for maintaining forests in a pristine condition. The immediate objective being addressed here is simply that of defining a level of resource harvest that can be sustained over time by the plant populations being exploited.
METHOD OF PRESENTATION
The report is divided into three main sections, each section treating a different
aspect of the ecology and exploitation of non-timber tropical forest resources:
Every attempt has been made to make the text as readable and as easily understood as possible. Definitions and supplementary material have been provided as hypertext links for easy reference. A list of pertinent references and relevent internet links are included at the end of each section for those readers desiring additional information on a particular topic.
SCOPE
The report is focused exclusively on non-timber plant resources, with particular
emphasis on trees. Crocodiles, butterflies, iguanas, turtles, bird's nests,
and the innumerable other animal resources and products collected from tropical
forests are not discussed here. The sustainability of harvesting forest fauna
is undeniably an issue of great importance. The basic ecology of plants and
animals is just too different to lump together in a work of this size.
Whenever possible, specific botanical examples are given to illustrate basic concepts. In view of the author's previous field experience, the majority of these examples have been taken from the tropical moist forests of South America and Southeast Asia. This geographical bias should not be taken to imply that there are no interesting or useful plants in the African tropics, that the problems of over-exploitation and resource depletion are absent from this region, or that the extensive dry forests found in more seasonal tropical environments are somehow unsuited for sustainable management.
The text is largely concerned with primary forests, either undisturbed or already subjected to some degree of exploitation, and the ways in which non-timber resources can be harvested from them with a minimum of ecological damage. The selective management of pioneer species, tree felling, or the deliberate creation of secondary vegetation within these forest areas are neither advocated nor discussed. The extensive areas of secondary forest that have been created throughout the tropics indeed represent an important source of non-timber products. A discussion of the use and management potential of these habitats, however, falls outside the scope of the present work.
A final comment. There is no question that economic, social, and political factors play an extremely important role in determining the success or failure of forest exploitation. This report, however, attempts to tell the story strictly from the plant's point of view. The reason why too many fruits are removed from the forest is not really the issue here. What we want to know is what happens as a result to the plant populations being exploited...and what can be done about it. The mechanics of over-exploitation are the same regardless of whether the fruits are collected by a village cooperative or a multi-national corporation, or whether the trees are growing in an extractive reserve, a state forest, or a logging concession.
In many areas occupied by traditional societies, management for NTFPs is part of traditional forest management, but new demands on forests are leading communities to seek more formal monitoring processes to guide the allocation and management of their shrinking biological resources. At the same time, managers of protected areas are seeking ways to accomodate the needs of traditional forest users while maintaining the integrity of the ecosystems that the protected areas were created to safeguard. To meet the widespread demand for formal guidance to determine ecological sustainable harvest levels for non-timber forest products, the Biodiversity Support Program (BSP) commissioned the production of Sustainable Harvest of Non-timber plant Resources in Tropical Moist Forest: An Ecological Primer.As is true for other guidance for ecological sustainability, this manual provides a subset of the necessary tools. The following discussion will provide the user of this manual with information about what the manual does and does not aim to accomplish.
The reader might think of this manual as a "toolbox" that provides simple and effective tools for the what and how of determining sustainable harvest levels of NTFPs in tropical moist forests. Biology is the ultimate determinant of sustainability-species and ecosystems die, survive, or flourish depending on whether their ecological requirements are met. Nature provides the grist to meet those requirements, but it is the mill of social organizations, individual decision makers, and markets-not nature-that determines whether the ecological requirements of species and ecosystems will be met. Thus, sustainability greatly depends on political, socioeconomic, and institutional factors.
To a large extent, the achievement of sustainability through the use of the biological monitoring tools in this manual will depend on who uses the tools. If the who includes local people and other forest users in the roles of decision- making planners and results analysts, then biological information developed from the toolbox will provide critical material for constructing a sustainable system for harvesting NTFPs. The tools can be applied in widely different situations. In some cases, government agencies will seek to use them to set harvest limits in state forest reserves; in other cases, community groups will use them to assess which of their forest's products offers the best option for sustainable, commercial harvests. In either case, the local forest users must cooperate in the application of the tools if sustainability is to be achieved.
It is, therefore, essential that the reader of this manual think about the who as well as about the what and how. Who will do this work, who will analyze the results, and who will benefit from sustainable harvests? Who is using the forest and for what purposes? What are their priorities? Other manuals are available to help answer these questions and to address other aspects of sustainable harvesting-for example, identifying or creating forest management committees, describing what kinds of information are essential for making decisions, or developing an appropriate process for making decisions on the basis of the information gathered.
This manual is meant to be used in an effort to plan and implement ecologically sustainable extraction of NTFPs. That effort must invoke the levels of user participation essential for (1) choosing products for increased extraction, and (2) monitoring the impact-two important steps for achieving sustainable harvests. The first decision will require an assessment of labor investment, economic and social feasibility, and other demands on the forest and its users. Users have important "indigenous knowledge" about the species, but more importantly, they are critical actors in both extraction and monitoring. They must be actively involved in the six steps outlined in the manual, not just used as a source of limited information.
For example, if this manual is being used by a project manager, the terms of reference he/she develops for analysis of ecological sustainability of a proposed project should include a Participatory Rural Appraisal (PRA) by the community to ascertain all the uses-present and planned-of the forest. The PRA should determine who makes decisions about forest management and who enforces those decisions. It should consider labor requirements and how they might conflict with existing or planned labor investment in other activities. User communities should rank the importance of NTFPs, both cash and non-cash benefits, as well as rank the importance of game, wood products, and the ecological services that they currently enjoy from the targeted forest. This information should be considered when choosing to increase levels of exploitation of one or more products and to evaluate the impacts of choosing one option over another. In addition, the decision-making body should consider the potential negative effects should the enterprise fail to be sustainable and decide whether the community wants to take that risk.
There is no recipe for achieving people's participation in any activity, just as there is no recipe for achieving ecological sustainability. Adding PRA to a project, for example, is not synonymous with achieving participation. Like the methods outlined in this manual, PRA is a tool. Following Borrini (1993), participation is a process by which people assess their needs and resources, recognize opportunities offered by projects, participate in planning and decision making, act and provide resources to implement projects, acquire benefits from projects, and develop partnerships with other project stakeholders. The steps that are necessary to achieve participation vary from project to project. Planning for participation is a serious part of project planning and requires investment of sign)ficant time and resources. If participation processes are fully established, the ecological monitoring processes described in this manual will provide participants with a powerful means to gain valuable information for sustainable forest-based enterprises.
BSP is also developing a Guide to Social Sustainability that will help project managers, aid agencies, and communities to identify the relevant social processes and organizations that should be engaged in and monitored for longterm ecological sustainability of conservation projects. Since this social primer is not yet complete, a short list of suggested readings is provided below. The two excellent manuals produced by the Joint Forest Management National Support Group in India (Poffenberger, et al., 1992) have combined participatory planning, monitoring, and assessment with tools for measuring biological factors at the local level. The manual from FAO/Bangkok (Borrini, 1993) provides practical guidance for incorporating participation into national level programs. The other books in the list offer specific advice for working with both local and national institutions and provide useful bibliographies.
Finally, the monitoring process described in this manual not only monitors the health of NTFP species, it also provides indicators that may function as an alarm system for telling the resource users that ecological changes are occurring. If the alarm is triggered, the changes may be caused by the NTFP harvest or some other factor. If regeneration is not occurring at the desired levels, users should examine the possibilities of excessive harvests as well as consider alternative explanations. This alarm system can be used to identify ecosystem-level problems only if those problems are causing a negative impact on the species in question. Whether negative changes at the ecosystem level will be mirrored by negative changes in the NTFP species will depend on the ecological role played by the species.
In order to maintain forests for their full range of benefits beyond NTFP production, the tools in this manual should be applied in conjunction with other tools to monitor ecosystem health, including methods developed by traditional societies and those developed by biologists. For example, monitoring the health of wildlife populations can provide an indicator of ecosystem health. The reading list below contains two methods source books for monitoring wildlife populations (Schemnitz, 1980; Caughley and Sinclair, 1994). These methods can be integrated with hunters' traditional methods for monitoring the health of game populations.
A healthy forest can provide many benefits for people. BSP hopes that this manual will help people to gain and apply new information about their forests. As always, BSP seeks feedback on this manual so that an improved second edition will include lessons learned by the manual's users. Spanish and French language editions will be available in 1995.
| -Janis B. Alcorn Biodiversity Support Program September 1994, Washington, D.C. |
Suggested readings to complement this manual:
Borrini, G. 1993. Enhancing People's Participation in the Tropical Forests Action Programme. Food and Agriculture Organization, Bangkok, Thailand.
Brown, M. and B. Wyckoff-Baird. 1992. Designing Integrated Conservation and
Development Projects. Biodiversity Support Program, World Wildlife Fund, Washington, D.C., USA (Available in English, French, and Spanish)
Caughley, G. and A.R.E. Sinclair. 1994. Wildlife Ecology and Management. Blackwell, Boston, Massachusetts, USA.
Cernea, M.M. 1985. Putting People First: Sociological Variables in Rural Development. Oxford University Press, New York, New York, USA.
Hope, A. and S. Timmel. 1984. Training for Transformation: A Handbook for Community Workers. Mambo Press, Gweru, Zimbabwe.
International Alliance of Indigenous-Tribal Peoples of the Tropical Forests. 1992. Charter of the Indigenous-Tribal Peoples of the Tropical Forest. (Available from Cultural Survival, 215 First Street, Cambridge, MA 02142, USA, or World Rainforest Movement, 8 Chapel Row, Chadlington OX7 3NA, UK)
Korton, D.C. and R. Klauss, eds. 1984. People-Centered Development: Contributions Toward Theory and Planning Frameworks. Kumarian Press, West Hartford, Connecticut, USA.
Poffenberger, M., B. McGean, A. Khare, and J. Campbell. 1992. Field Methods Manual II. Community Forest Economy and Use Patterns. Society for Promotion of Wastelands Development, Joint Forest Management National Support Group, New Delhi, India. (Available at no cost from Ford Foundation, 55 Lodi Estate, New Delhi - 110 003, India)
Poffenberger, M., B. McGean, N.H. Ravindranath, and M. Gadgil. 1992. Field Methods Manual 1. Diagnostic Tools for Supporting Joint Forest Management Systems. Society for Promotion of Wastelands Development, Joint Forest Management National Support Group, New Delhi, India. (Available at no cost from Ford Foundation, 55 Lodi Estate, New Delhi - 110 003, India)
Schemnitz, S.D. 1980. Wildlife Management Techniques Manual. The Wildlife Society, Washington, D.C., USA
Uphoff, N. 1986. Local Institutional Development: An Analytical Sourcebook with Cases. Kumarian Press, West Hartford, Connecticut, USA.
For useful newsletters and publication series, write to:
Biological Diversity Handbook Series, Smithsonian Institution Press, Department 900, Blue Ridge Summit, PA 17294-0900, USA. (Currently the only volume available is Measuring and Monitoring Biological Diversity: Standard Methods for Amphibians)
Forest, Trees and People Program, Community Forestry Unit, Forestry and Planning Division, Forestry Department, FAO, Via delle Terme di Caracalla, I~0100 Rome, Italy. (FTP Newsletters available in French, Spanish or English; several publication series)
The Forest Stewardship Council-contact Michael Kiernan, WWF, 1250 24th Street, NW, Washington, DC 20037, USA or Timothy Synnott, Executive Director of The Forest Stewardship Council, Avenida Hidalgo 502, 68000 Oaxaca, Oaxaca, Mexico. (For information on "Principles and Criteria for Natural Forest Management")
International Institute for Environment and Development (IIED), 3 Endsleigh St., London, WCIH ODD, UK (Participatory Rural Appraisal newsletters and publications)
Species Survival Commission Specialist Group on Sustainable Use of Wild Species, IUCN, Rue Mauverney 28, CH-1196 Gland, Switzerland. (Developing guidelines for sustainable use of wildlife)
The controlled exploitation of non-timber forest products holds great potential as a method for integrating the use and conservation of tropical forests. This report attempts to narrow the gap between the potential and the reality of this land-use practice. The main objective is to give a concise overview of the ecology, exploitation, and management of non-timber tropical forest plant resources in terms that can be easily understood by non-specialists.
The report is divided into three main sections. Section I summarizes the principal ecological characteristics of tropical plants that limit the nature and intensity of resource exploitation. Section II discusses the potential long-term ecological impacts resulting from the harvest of different plant parts. Section III presents a general strategy for managing non-timber plant resources on a sustained-yield basis. Within the context of the report, a sustainable system for exploiting non-timber resources is defined as one in which fruits, nuts, latexes, and other products can be harvested indefinitely from a limited area of forest with negligible impact on the species being exploited.
The report focuses exclusively on the ecological context of non-timber tropical forest products, with particular emphasis on the structure and dynamics of tree populations. It does not address the innumerable economic and social factors which are also important in determining the overall sustainability of forest resource exploitation.
2. Tropical trees vary greatly in terms of the timing, duration and intensity of flowering and fruiting. Very few tropical forest species produce reliable fruit crops during a well-defined, predictable season each year.
3. The great majority of tropical trees rely on animals to pollinate their flowers and disperse their seeds. Any serious program of commercial resource exploitation must include measures to conserve viable populations of these animals.
4. There is a high probability that a seed will come in contact with an animal during the time between seed dispersal and seed germination. In most cases, this encounter proves fatal for the seed. In terms of total numbers, seed predation is one of the most severe sources of mortality during the life of a plant. Mortality is still extremely high following germination, and over 90% of the new seedlings may die before becoming established in the understoy. Only a very small fraction of these seedlings (less than 1 in 1,000,000 for some species) will ever make it to the canopy and produce fruit.
5. The regeneration of many forest species is linked to the occurrence of canopy gaps. Based on the gap requirement and general shade tolerance of different species, three regeneration types of 'guilds" can be recognized: (1) early pioneer species, (2) late secondary species, and (3) primary species. The establishment, growth, reproduction, longevity, and management potential of the species in each group are markedly different.
6. The population structure or size-class distribution of tropical trees can be described by three basic types. A Type I structure is displayed by populations that maintain a more or less constant rate of seedling establishment. A Type II structure is characteristic of populations that experience sporadic or irregular seedling establishment. The final type of population structure, Type III, reflects a species whose regeneration is severely limited for some reason. Although these three types correlate well with the regeneration guild of a species, a single species may exhibit any of these types depending on the environment and its current rate of seedling establishment.
8. Given that the initial impact of resource extraction is determined largely by the specific type of resource or plant tissue harvested, the enormous variety of non-timber plant resources produced by tropical forests can be grouped into three major categories: (1) fruits and seeds, (2) plant exudates (e.g. latexes, gums and resins), and (3) vegetative structures (e.g. stems, leaves, roots, barks, and buds).
9. Although unnecessary, many fruits and seeds are currently harvested by felling the tree. This practice has led to the serious depletion of several important fruit and oil seed-producing species. Even in the absence of destructive harvesting, the collection of commercial quantities of fruits and seeds can cause notable changes in the structure and dynamics of a tree population. These changes are typically precipitated by a reduction in seedling establishment due to over-harvesting. If uncontrolled, this process can result in the gradual extinction of the population under exploitation.
10. When properly conducted, the extraction of plant exudates does not disturb the forest canopy, kill the exploited tree, or remove its seeds from the site. There are, however, several examples of exudate-producing trees that are harvested destructively, and even the non-destructive tapping of rubber can cause a reduction in the growth and reproduction of wild Hevea trees.
11. The harvest of vegetative structures produces one of two different impacts. The plant species will either be killed in the process, or, in a limited number of cases, it will survive and later regenerate the vegetative structure removed. Rattan is a well-known example of the former scenario, and uncontrolled harvesting is rapidly depleting this non-timber resource in Southeast Asia. Leaves and buds are examples of vegetative structures that regenerate after harvesting.
13. The complete process of sustainable exploitation is composed of six basic operations or steps: (1) species selection, (2) forest inventory, (3) yield studies, (4) regeneration surveys, (5) harvest assessments and (6) harvest adjustments. The actual sequence of operations is not fixed and can be adapted to a variety of different situations.
14. Species selection will be based largely on economic and social criteria. A third criterion that should also be considered is the overall potential of the resource to be managed on a sustained-yield basis. Although the fact is frequently overlooked, some forest species are inherently better able to withstand the continual perturbations caused by resource extraction than others. Important ecological factors to consider include the life cycle characteristics of the species (e.g. phenology of flowering and fruiting, pollination, and seed dispersal), the type of resource produced, its abundance in the forest, and the size-class distribution of natural populations.
15. Density and size-class structure data are the most fundamental pieces of information required for management. The collection of these data requires a quantitative forest inventory. The inventory should provide an estimate of the total number of harvestable trees per hectare in different forest types and should document the existing size-class distribution of adult trees. These data will be used to construct a size- class histogram for the species being harvested. It is strongly recommended that a professional forester or inventory specialist be involved in the planning and execution of this fieldwork.
16. Yield studies are conducted to estimate the total quantity of resource produced by trees of varying size. Just as foresters use growth data to avoid cutting timber faster than it is produced in the forest, the sustained- yield management of non-timber resources also requires information about the productive capacity of the species being exploited. Probably the easiest way to obtain production data is to train local collectors to weigh, count, or measure the quantity of resource produced by different sample trees during harvest season. These studies should be repeated every few years using the same group of sample plants to monitor the variation in yield over time.
17. Periodic regeneration surveys are used to quantify the initial density of seedlings and saplings in the populations being exploited, and to monitor the way in which these densities fluctuate in response to differing harvest levels. The results from these surveys are divided into height classes and then added to the size-class histograms constructed from the inventory results to provide a complete picture of population structure from seedlings to large adult trees. Repeating these surveys every five years is probably sufficient for most species.
18. Harvest assessments are visual appraisals of the behavior and condition of adult trees that are conducted concurrently with harvest activities. In many cases, these quick assessments can detect a problem with reproduction or growth before it becomes serious enough to actually reduce the rate of seedling establishment.
19. The seedling and sapling densities recorded in the original regeneration survey are used as the threshold values by which sustainability is measured. As long as densities remain above these values, and no major problems are detected in the harvest assessments, there is a high probability that the current level of exploitation can be sustained. If seedling or sapling densities are found to drop below this value, however, immediate steps should be taken to reduce the intensity of harvest. Two different procedures are described to make these harvest adjustments. The first method regulates the number or size of the plants being exploited. The second method limits the total area from which the resource can be harvested. For populations that have never been exploited before, a good first approximation is to extract no more than 80% of the total harvestable yield during the first collection cycle.
20. The six-step management strategy provides a simple and effective method for achieving a sustainable harvest of most non-timber forest products. In some cases, however, a more intensive form of management may be required. If, for example, seedling densities continue to drop in spite of drastic harvest reductions, or productivity declines, or trees start to die, some form of remedial treatment should be initiated as soon as possible.
Potential courses of action include enrichment planting, selective weeding, and the cutting and removal of woody vines.
In a very basic sense, tropical forest trees are really no different than any other type of plant. Their seeds germinate, they grow, they flower, they produce fruit, and eventually they die. What makes tropical trees unique -- and the object of so much scientific inquiry and public concern -- is the amazingly complex and diverse ways in which they accomplish these routine life functions. Put a large number of these trees together, each species germinating, growing, flowering, and fruiting in a different way, at different times and with varying degrees of success, and you have some idea about why we understand so little about the ecology of tropical forests. What we do know at this point, however, is that most tropical forests exhibit several ecological characteristics that make sustainable harvesting more elusive than it might first appear.
TREE DENSITY AND ABUNDANCE
One of the most fundamental and well-known characteristics of tropical forests
is the large number of species that grows in them. To illustrate this point
specifically for trees, floristic data collected from small tracts of tropical
forest in Amazonia and Southeast Asia are presented in Table 1. Although there
is quite a bit of variability in the estimates from different sites, it is clear
that the tropical forests in both regions are extremely diverse and may contain
from 100 to almost 300 different tree species in a single hectare. To put this
in perspective, a mixed hardwood forest in the northeastern United States contains
about 17 tree species per hectare (one hectare=10,000m2
or 2.47 acres).
Table 1. Total number of tree species larger than 10.0 cm in diameter (DBH) within small plots of tropical forest in Amazonia and Southeast Asia.
| Site | Soils/Habitat | Area | No. Species |
| Amazonia | |||
| Yanamono, Peru | Alluvial sediment | 1.0 ha. | 283 |
| Mishana, Peru | White sand | 1.0 ha. | 275 |
| Rio Xingu, Brazil | Upland forest | 1.0 ha. | 162 |
| Breves, Brazil | Upland forest | 1.0 ha. | 157 |
| Para, Brazil | Flooded forest | 1.0 ha. | 103 |
| Southeast Asia | |||
| Gunung Mulu, Sarawak | Alluvial sediment | 1.0 ha. | 225 |
| Gunung Mulu, Sarawak | Red-yellow clay | 1.0 ha. | 215 |
| Wanariset, Kalimantan | Upland forest | 1.0 ha. | 180 |
| Andalau, Brunei | Upland forest | 1.0 ha. | 140 |
| Raya-Pasi, Kalimantan | Upland forest | 1.0 ha. | 135 |
From a management standpoint, the high species diversity exhibited by tropical
forests is a two-edged sword. On the positive side, the large number of different
plant species present frequently implies that there is an equally large assortment
of useful plant resources available. It has been estimated, for example, that
one out of every six species found in the lowland forests of Southeast Asia
produces an edible fruit, nut, oil seed, medicine, latex, gum or other non-timber
forest resource. In most of the tropical areas where this has been studied,
"resource richness" is a direct consequence of high species diversity.
Unfortunately, an additional consequence of high species diversity is that the individuals of a given species usually occur at extremely low densities. There is a limit to the total number of trees per hectare that can be packed into a tropical forest. If you have a large number of species, each species can only be represented by a few individuals.
This trend of high species diversity coupled with low species density has been repeatedly documented in tropical forest inventories. The results from two such inventories, one conducted in Brazilian Amazonia and the other from Pasoh Reserve on the Malay Peninsula, are shown graphically in Figure 1. As the histogram clearly documents, the great majority of the tree species at both sites are represented by only one or two individuals. Less than ten percent of the species had populations with more than four trees per hectare.
Figure 1. Densities of different tree species within 3.0 hectare tracts of tropical forest in Amazonia and Southeast Asia.
The basic problem here is straightforward. Tropical forests contain a lot of different species. Although many of these species produce valuable non-timber products, most of the trees of interest are scattered throughout the forest at very low densities. Low density resources are difficult for collectors to locate, require long travel times, produce a low yield per unit area, and are extremely susceptible to over-harvesting.
It is important to note that there are numerous exceptions to the rule of high species diversity in tropical forests. Although the fact is seldom mentioned in much of the current literature, dense aggregations of a single tree species are known to occur in habitats where severe flooding, shallow soils, or frequent disturbance preclude the formation of species-rich forest. These oligarchic forests (Gr. oligo= few, archic= dominated or ruled by) have been reported from almost every region of the wet tropics. The extensive stands of aguaje palm found in the lowlands of Amazonia are notable examples of this type of forest.
In terms of tree density and yield, oligarchic forests rival many of the commercial plantations that have been established in the tropics. Given their wide distribution, productivity, and relative ease of harvest, these unique plant communities would seem to have great potential for supporting a program of sustainable resource exploitation.
FLOWERING, FRUITING, AND REPRODUCTIVE DYNAMICS
The different ways in which tropical trees produce their flowers and fruits
can be a major stumbling block to resource exploitation. This unavoidable fact
of life is perhaps most obvious in those cases where the actual resource of
interest is a fruit or a seed, and where the seasonality and magnitude of fruit
production have a direct impact on harvesting. It should be remembered, however,
that fruits contain the seeds necessary for a species to regenerate and maintain
itself in the forest. Irrespective of the species or type of resource being
exploited, plant reproduction is a key issue in sustainability.
PHENOLOGY OF FLOWERING AND FRUITING
Phenology refers to the timing or seasonality of specific biological events
(e.g. leaf fall, growth or, as in this case, the production of flowers and fruits.)
Detailed studies of flowering and fruiting phenology have been conducted in
almost every area of the tropics. The results from these studies have shown
that tropical trees vary greatly in terms of the timing, duration and intensity
of flowering and fruiting. Different species may produce flowers annually, supra-annually,
i.e. with an interval of several years between flowering events, or even several
times a year. The periodicity of fruit production exhibits similarly complex
patterns. Very few tropical forest species produce reliable fruit crops during
a well-defined, predictable season each year.
One of the most interesting examples of supra-annual flowering and fruiting is exhibited by the Dipterocarpaceae, a large family of dominant canopy trees in Southeast Asia. At irregular intervals of from two to ten years, numerous dipterocarp species will more or less simultaneously start to flower within the forest. This mass flowering phenomena is usually followed by an extremely abundant level of fruit production known as mast fruiting. In an especially intense mast year, almost every dipterocarp and up to 80% of all canopy trees may burst into flower.
The exploitation and management of tropical forests would be considerably easier if the production of flowers and fruits occurred on a more predictable basis. In fact, it is hard to imagine a more difficult management situation than one in which the key species produce fruit at irregular intervals of from two to ten years. This, however, is exactly the framework within which the illipe nut trade in northwestern Borneo is forced to operate.
POLLINATION
The low density and scattered distribution of individuals in most tropical tree
populations represents a dilemma for pollination. How do you move pollen effectively
from the flowers of one tree to another when the distance between these individuals
may be in excess of 100 meters? A brief look at Table 2, which lists the principal
pollinators of twelve commercially important tropical trees, suggests the answer
to this question.
Table 2. Pollinators of a selected number of tropical plant resources. Animals listed represent principal pollinators; the flowers of each species may also be visited by other animals.
| Species | Common Name | Use | Pollinator |
| Shorea spp. | Illipe nut | oil seed | thrips |
| Hevea brasiliensis | Rubber | latex | thrips/midges |
| Theobroma cacao | Cacao | oil seed | midges |
| Mangifera indica | Mango | edible fruit | flies |
| Artocarpus heterophyllus | Jackfruit | edible fruit | flies/beetles |
| Orbignya martiana | Babassu | oil seed | beetles |
| Bactris gasipaes | Peach palm | edible fruit | beetles |
| Bertholettia excelsa | Brazil nut | edible seed | bees |
| Euterpe oleracea | Açai | edible fruit | bees |
| Ceiba pentandra | Kapok | fiber | bats |
| Durio zibethinus | Durian | edible fruit | bats |
| Parkia speciosa | Petai | edible fruit | bats |
Tropical trees have evolved relationships with a variety of animals, ranging
from tiny thrips and midges to bees and large bats, to shuttle pollen between
trees. These relationships can be quite specific, with one type of insect being
solely responsible for pollinating the flowers of a particular forest species.
It is important to emphasize that these plant-animal interactions are not simply
isolated anecdotes from tropical forest folklore. The large majority of tropical
trees rely exclusively on animals to transfer their pollen. One study conducted
within a small tract of lowland forest in Costa Rica found that 139 (96.4%)
of the 143 tree species surveyed were pollinated by animals.
There is an important lesson to be gained from these findings: no pollinators, no fruits; no fruits, no seedlings; no fruits or seedlings, no products or profit. Any serious program of commercial resource exploitation conducted in tropical forests must necessarily include measures to insure adequate pollination. In some cases, this requires a greater appreciation of the fact that land-use practices far away from the immediate harvest site can be extremely disruptive to populations of wide-ranging animals such as bats or even bees. The current situation with the nectivorous bat, Eonycteris spelaea,provides a dramatic, yet unfortunate, example of this.
Eonycterisbats are apparently the exclusive pollinators of durian trees in Peninsular Malaysia. These bats, however, feed preferentially on the flowers of Sonneratia alba,a coastal mangrove which occurs in dense groves and produces a few large flowers continually throughout the year. In order to forage on this reliable food source, the bats fly 20 to 40 kilometers from their roost each night. During this journey to the coast, any durian trees that they may encounter are pollinated almost as a dietary afterthought. Any attempt to maintain a viable population of these important pollinators in Malaysia must inevitably address the fact that the principal food source of Eonycteris spelaeais currently being decimated by coastal development.
SEED DISPERSAL
The importance of animals in the reproductive biology of tropical trees does
not end after pollination. Once fruits and seeds have been successfully nurtured
to maturity, the next problem faced by flowering plants is what to do with these
offspring. Given the incredible variety of different fruit types produced by
tropical trees, many of them extremely rich in protein, starch, or sugar and
quite "costly" for the plant to produce, it is clear that these fruits have
not evolved to simply drop to the ground beneath the parent tree. It seems more
likely that these fruits have been specifically designed to be eaten -- to be
eaten, and the intact seeds within the fruit effectively dispersed to a new
location.
Seed dispersal offers at least three ecological benefits to a plant. A dispersed seed has a greater probability of escaping the excessive crowding and mortality that invariably occurs under the crown of the parent tree. Dispersal may also allow a seed to spread its species into new habitats. Finally, some types of dispersal may position a seed in the precise site required for successful germination and growth.
These benefits are not mutually exclusive, and all three may occur depending on the plant species, the dispersal agent and the immediate environment. There is, however, an ecological cost associated with seed dispersal, especially when animals are involved. During the process of handling, transporting, or feeding on fruits, frugivores may destroy a large proportion of the seeds inside.
The large number of tropical trees with animal-dispersed fruits suggests that the actual costs of using these dispersal agents are greatly outweighed by the potential benefits. Research conducted in the tropical forests of Central and South America indicate that over 90% of the canopy trees produce fruit adapted for consumption, and subsequent dispersal, by animals; related studies in Southeast Asia have produced similar results. Clearly, bats, birds, primates, peccaries, fish and a wide assortment of other vertebrates are responsible for moving an enormous quantity of seeds around in a tropical forest. These animals may either remove fruits directly from the tree, or they may forage on fruits which have already fallen to the ground.
The presence of fruit-eating animals in a tropical forest can be a problem for commercial collectors. These animals damage or consume large quantities of fruit, and their activities quickly become a nuisance when the species being eaten is an economically important one. In those cases where collectors and frugivores are actively competing for the harvest of the same species, the animals invariably get there first. It is not surprising that a common solution to this problem has been simply to eliminate the animals from the forest.
It is worth remembering, however, that forest frugivores play an important role in dispersing the seeds of many commercial tree species. The seeds of some species, in fact, will not even germinate without first being cleaned by animals. The distribution and abundance of the seedlings produced by a forest species are frequently controlled by the action of dispersal agents, and, like it or not, the great majority of these dispersers are animals. Failing to conserve viable populations of these animals would be a serious management error.
REGENERATION AND GROWTH
Safe arrival from the parent tree to the forest floor does not, by any means,
guarantee that a seed will germinate and become established in the understory.
The seed must avoid being eaten, it must encounter the appropriate light, moisture,
and nutrient conditions for germination, and it must be able to germinate and
grow faster than the seeds of all the other species that are trying to establish
themselves on the same spot.
There is a high probability that a seed will come in contact with an animal during the lapse between dispersal and germination. In most cases, this encounter proves fatal for the seed. In terms of total numbers, seed predation is unquestionably one of the most severe sources of mortality during the life of a plant. Over 98% of the seeds of some forest species are lost to predation; rodents, beetles, ants, and weevils are the most frequently cited seed destroyers.
Even assuming that a seed has successfully germinated and a new seedling has put down roots and unfurled its first new leaves, there is still very little chance that the plant will become established on that site. The first year of life for a seedling is plagued with problems. To begin with, light levels in the forest understory are usually so low (1 to 2% that of full sun) that it is difficult for the seedling to grow. Added to this is a very high probability that it will be browsed on by an animal, outcompeted by its neighbors, smashed by a falling branch, attacked by fungal pathogens, ripped out of the soil by a rolling rock, or wilted by wildly fluctuating moisture levels.
A graphic example of the severe mortality experienced by tropical tree seedlings during their first year is provided by the three survivorship curves shown in Figure 2. Brosimum alicastrumis a widely distributed canopy tree in Central and South America; Shorea curtisiiand Shorea multifloraare both common components of mixed dipterocarp forest in Southeast Asia. As the name implies dipterocarp forests are dominated by trees from the Dipterocarpaceae family.
Figure 2. Seedling survivorship curves for Shorea curtisii,S. multifloraandBrosimum alicastrum.All three species are primary forest trees.
As is illustrated in this figure, seedling survivorship by these three species after 12 months ranges from a high of 22% for S. curtisiito a low of only 3% for B. alicastrum.Five months after germination over 50% of the seedlings of each species have already died. Taking into account seed predation and lack of germination, less than 0.1% of the seeds produced by B. alicastrumbecome established seedlings. Only a very small fraction of these seedlings (approximately 1 in 1.5 million) will ever make it to the canopy and produce fruit. Data such as these, which are by no means atypical of tropical trees growing in primary forest, provide a convincing demonstration of how difficult it is for a tree population to maintain itself in the forest -- even in the absence of any type of resource harvesting.
CANOPY GAPS
The excessive seedling mortality that characterizes the regeneration of many
forest species raises an important management question. Where are the few seedlings
located that actually survive? What type of site provides the necessary conditions
for seed germination, and also allows the new seedling to express an optimal
rate of growth relative to its neighbors? The specific combination of environmental
conditions which describe such a site may be thought of as the regeneration
nicheof a species. To a large extent, the area and distribution of these
niches are what regulate the number of seedlings that become established in
the forest.
Extensive research on seedling establishment has shown that the regeneration niches of a large percentage of tropical trees have one feature in common -- they are all in some way related to the sporadic occurrence of treefalls. Tropical trees may blow down, get struck by lightning, or simply die from old age and fall down. Each of these events produces an opening or "gap" in the forest canopy that allows direct sunlight to enter the understory. In addition to the increased sunlight, canopy gaps also exhibit lower humidity, higher temperatures, and higher soil moisture levels than those found under a closed canopy.
These abrupt changes in the understory environment have a notable effect on most of the seedlings in the vicinity of a canopy gap. In smaller gaps, many of the more shade-tolerant seedlings which have managed to survive under a closed canopy will display a significant increase in growth in response to the higher light levels. Numerous canopy species exhibit this behavior. Their seeds germinate in the shade and the young seedlings grow until they have produced about two or three leaves. The seedlings then appear to enter a state of suppression in which they exhibit little or no height growth. There are only two possible outcomes to this physiological condition. The seedlings slowly die over time, or they are "released" by the occurrence of a canopy gap overhead.
In larger gaps, the drastic increase in light level and soil temperature may trigger the germination and growth of light-demanding species. The seedlings of these species grow extremely fast under sunny conditions, and large gaps are soon swamped with these aggressive, "weedy" plants. Any shade-tolerant species which may occupy the site are soon outcompeted. Classic examples of light-demanding species include Ochroma lagopus(balsa wood) and Cecropiain the American tropics, and many of the over 250 species of Macarangafound in Southeast Asia.
Canopy gaps play a critical role in the establishment and growth of tropical trees; up to 75% of the canopy trees in some areas require the occurrence of a treefall for seedling establishment. The problem is that there is absolutely no way to predict exactly when and where a canopy gap will be created. There is also no guarantee that the desired species will actually colonize a gap should it occur.
REGENERATION GUILDS
Tropical trees have evolved an incredible variety of different life strategies
to pollinate their flowers, to disperse their seeds, and to enhance the establishment
of new seedlings into their populations. It has long been noted, however, that
there are certain similarities and patterns in these strategies which allow
tropical species to be grouped into distinct ecological categories. Light tolerance
(i.e. shade-tolerant or light-demanding), for example, is one of the most frequent
ecological characteristics used to group species. The reason for grouping species
is not to obscure the inherent diversity of different strategies found within
a tropical forest. Rather, these categories provide a useful tool for more rapidly
understanding the basic ecological requirements of a forest species.
For the purpose of this report, it is useful to define three groups or "guilds" of forest species based on their regeneration characteristics, growth rate and life span. These three regeneration guilds are: (1) primary, "climax", or mature forest species, (2) early pioneer or "secondary" species, and (3) late secondary species. In spite of the names applied to these different groups, all three types can occur in mature tropical forest. A schematic listing of the basic ecological characteristics of each guild is presented in Table 3.
Table 3. Basic ecological characteristics of early pioneer, late secondary, and primary tropical forest species
| Character | Early Pioneer | Late Secondary | Primary |
| Distributiion | very wide | very wide | usually restricted: many endemics |
| Seed dormancy | well-developed | slight to moderate | none |
| Seed or fruit size | small | small to intermediate | large |
| Seed dispersal | birds, bats, wind | mainly wind, but also mammals | mammals, birds |
| Shade tolerance | very intolerant | intolerant | seedlings very tolerant, later intolerant |
| Gap size required | large | intermediate | small |
| Seedling abundance | very scarce | usually scarce | abundant |
| Growth rate | very fast | fast | slow to very slow |
| Wood density | light | light to medium | very hard |
| Life span | 10 to 25 years | 40 to 100 years, sometimes more |
100+ years |
Primary tree species germinate in the shade and can survive in the understory
for a considerable length of time until a canopy gap opens overhead. Their seeds
are usually large and few, with abundant seed reserves and little or no dormancy.
These species, as a group, are highly shade-tolerant and possess a photosynthetic
system adapted for growth under very shady conditions. Growth is relatively
slow and wood density, as a result, can be extremely high. Primary trees may
live for several hundred years and attain heights of over 60 meters. Many valuable
tropical hardwoods fall into this guild, together with several important fruit
and oil-seed trees. Many understory palms and herbs are also primary species.
Early pioneers frequently persist for long periods in the soil as dormant seeds. Their seeds, which are small and produced in abundance, require the stimulus of a large gap opening (i.e. increased soil temperature or light intensity) to germinate. After germination, these species exhibit high maximum rates of photosynthesis and growth. Wood density is correspondingly light. Early pioneer tree species mature rapidly, reproduce early, and die young (circa 10 to 25 years).
Late secondary plants represent an intermediate guild between primary and early pioneer species. These species are typically light-demanding, but their seeds do not exhibit the stringent dormancy of early pioneers and smaller gap sizes are required for germination. Seed dispersal into gaps is facilitated by wind, birds, bats, or ground mammals. Late secondary species exhibit the fast growth and maximal photosynthesis of many pioneer species, but they grow to a much larger size and persist for longer periods in the canopy. Wood density is variable, but usually lower than that of primary species.
Every plant does not fall neatly into one of these groups. There are varying degrees of shade tolerance and a complete spectrum of responses to varying degrees of light, soil moisture, and competition from other species. Even within a single species, the genetic make-up of different individuals can cause great variability in growth rate, wood density, fruit production, seed germination and seedling establishment. A true understanding of the ecological behavior of a species can only be gained through careful observation and detailed study. Such an effort, however, is highly warranted. Sustainable resource use hinges on a species' ability to continually establish new seedlings while being subjected to repeated and intensive harvesting. A basic knowledge of its regeneration and growth requirements can greatly facilitate this process.
POPULATION STRUCTURE
The ultimate criteria by which the life strategy of a species must be measured
is its effectiveness in "recruiting" new individuals into its population. The
more effective this strategy, the longer the population will be able to maintain
itself in the forest. One method of measuring this success is to monitor the
frequency and abundance of seedling establishment over a period of several decades,
and to record the resultant increase or decrease in population size over time.
Fortunately, it is not always necessary to conduct this laborious and time-consuming
procedure. In many cases, the recruitment history of a particular species is
reflected by the size distribution of individuals within its population. A rapid
appraisal of population structure can frequently provide information about whether
or not a species is regenerating itself in the forest.
Population structure data have long been used by foresters and ecologists to study the regeneration dynamics of forest species. The results from these studies have shown that the structure of most tree populations can be described by a limited number of size-class or diameter distributions. Three of the most common types of population structure are shown in Figure 3.
Figure 3. Three idealized size-class distributions exhibited by tropical tree populations. Size-class intervals are 10 cm DBH.
The Type I size-class structure displays a greater number of small trees than large trees and an almost constant reduction in the number of trees from one size class to the next. This type of population structure is characteristic of shade-tolerant, primary species which maintain a more or less constant rate of seedling establishment. In these populations, it is pretty safe to assume that the death of an adult tree will, at some point, be replaced by individuals growing up from the smaller size classes. A Type I structure is thought by many authors to represent the ideal of a stable, self-maintaining population. This is the type of structure that you strive to preserve in natural populations of non-timber forest resources.
A Type II size-class structure is characteristic of populations which experience sporadic or irregular seedling establishment. The actual level of regeneration may be sufficient to maintain the population, but its infrequency of occurrence causes notable "peaks" and "valleys" in the size-class distribution as the new seedlings grow into larger size classes. This type of distribution is common among late secondary species that depend on canopy gaps for regeneration. It may also reflect a population whose regeneration has been temporarily interrupted through excessive harvesting of fruits or seeds, direct physical damage to seedlings (e.g. trampling by collectors), or lack of pollinators or dispersal agents.
The final size-class distribution, Type III, reflects a species whose regeneration is severely limited for some reason. Most of the individuals in these populations are more or less the same size, and although many of them may be producing flowers and fruits, no seedlings have been successfully established. Type III population structures are frequently encountered among light-demanding, early pioneer species which require large canopy gaps for regeneration. In the absence of such a disturbance, these species may temporarilydisappear from the forest -- the former population represented only by the seeds lying dormant in the soil. A Type III distribution is not restricted to early pioneer species. Populations of late secondary or primary species can also exhibit this pattern if seedling establishment is interrupted for a long enough period of time. Unless conditions change, these populations will permanentlydisappear from the forest.
Although the three size-class distributions correlate well with the three different regeneration guilds, it is important to remember that the population structure of a species is extremely dynamic and sensitive to changes in the level of regeneration. A Type I distribution can easily change into a Type II if existing rates of seedling recruitment are reduced. Further constraints on regeneration may drive the population to a Type III distribution. Given this behavior, it is most useful to view the three structural types as a single sequence through which a population passes on its way to extinction. The occurrence of a Type III structure in a population of shade-tolerant, primary trees, for example, is a sure sign that something is wrong.
Although necessarily brief, the preceding discussion has attempted to show that tropical forest species display a variety of different ecological characteristics that can make sustainable harvesting a very difficult objective to achieve. The major problem areas are:
LITERATURE
Several excellent textbooks are available to readers desiring further information
about the ecology of tropical trees and forests. A few examples are cited below:
The aguaje palm (Mauritia flexuosa) is a massive tree common throughout lowland Amazonia; pure stands of this palm extend over a million hectares in Peru alone. Its fruits are eaten raw or processed into a sweet paste for beverages and ice creams. The fruits and seeds also yield an edible oil of good quality.
The Biodiversity Support Program (BSP) was established in 1988 with funding from the Research and Development Bureau of the U.S. Agency for International Development (USAID)., under cooperative agreement number DHR-5554-A-00-8044-00. BSP is implemented by a consortium of World Wildlife Fund, The Nature Conservancy, and the World Resources Institute. The central purpose of the program is to support efforts to conserve biological diversity in developing countries through information, networking, pilot implementation projects, and research and analysis of conservation and development techniques.
Durian (Durio zibethinus) is unquestionably the premier market fruit in Southeast Asia. Some describe it as the most delicious fruit in the world; others have suggested that the flavor is a little like eating french custard in a latrine. This undeniably smelly fruit resembles a football covered with sharp, woody spines.
The reader is strongly advised to look beyond the examples and to focus on the underlying concepts being illustrated. Tropical moist forests contain different species and exhibit different ecological characteristics than tropical dry forests, but the basic procedures required to achieve a sustainable harvest are essentially the same in each environment. Similarly, an understanding of population density and yield is as important for managing herbaceous plants, shrubs, and lianas as it is for trees.
A somewhat curious example of seed dispersal by animals has been observed in tropical riverine forests. A large proportion of the trees in these seasonally flooded habitats drop their fruits directly into the water. These fruits are eaten by fish which eventually defecate the seeds, usually after swimming a considerable distance.
Illipe nut is the commercial name for the winged fruits produced by about 20 different species of Shorea trees. The seeds from these fruits contain an oil whose chemical and physical properties are remarkably similar to cocoa butter. The oil content of some seeds may be as high as 50%. Large quantities of illipe nuts are collected and sold to be used in the manufacture of chocolate, soap and cosmetics. In 1987, a recent mast year, over 13,000 tons of illipe nuts valued at over 5 million dollars (US) were exported from West Kalimantan, Indonesia alone. Less than 50 tons were collected the following year. The Dayak children shown to the left are holding the fruits of Shorea macrophylla, or tengkawang tungkul as it is known locally.
Light-demanding species are specifically adapted for growth and reproduction under high light levels. Large, lobed leaves, such as those exhibited by the Cecropia sapling shown to the left, are a common feature of these plants.
Non-timber forest products are biological resources other than timber which are harvested from either natural or managed forests. Examples include fruits, nuts, oil seeds, latexes, resins, gums, medicinal plants, spices, wildlife and wildlife products, dyes, ornamental plants, and raw materials such as bamboo and rattan. The fruits shown on the left, rambutan (Nephelium lappaceum), tampui (Baccaurea motleyana) and lansat (Lansium domesticum), are valuable non-timber resources in Kalimantan (Indonesian Borneo).
The term plant population refers to a group of plants of the same species growing together within a limited area of forest. In the ecological hierarchy, this level of resolution falls between the individual and the community. Much will be said about plant populations in this report because it is at this level that the effects of harvesting are most readily visible.
Seed predation refers to the destruction of seeds by animals that attack, eat, lay eggs on, or otherwise damage them.
Shade-tolerant species possess certain physiological adaptations (e.g. enhanced photosynthetic system) that better enable them to survive in the shade. Photo shows Brosimum alicastrum seedlings growing in the understory of a tropical forest in Veracruz, Mexico. The seedlings are experiencing a brief period of sunflecks.
Sustainability is a tricky word. Although there appears to be a general consensus that the exploitation of tropical forests should embody this concept, there is a considerable degree of confusion about what the word actually means. Within the present context, sustainability will be defined in a restricted ecological sense. From an operational or management perspective, a sustainable system for exploiting non-timber forest resources is one is which fruits, nuts, latexes, and other products can be harvested indefinitely from a limited area of forest with neglible impact on the structure and dynamics of the plant populations being exploited.
For those who want to know a little bit about me, I studied forestry at the University of Arkansas and received my Masters and Ph.D. in plant ecology from the Yale School of Forestry and Environmental Studies. I have been investigating the ecology, use, and management of tropical forest resources for more than 15 years. My fieldwork has taken me to two of the largest and least explored tropical regions in the world, lowland Amazonia and the island of Borneo, as well as to the managed forest of Mayan Mexico. I am the author of numerous scholarly papers and articles and have written two books on the sustainable exploitation of rain forest resources. I am currently the Kate E. Tode Curator of Botany in the Institute of Economic Botany of The New York Botanical Garden. I can be contacted at (cpeters@nybg.org), and I would welcome any comments (brief ones, please) that you have about the sustainability primer. Thanks for your interest....
Charles M. Peters, Ph.D.
This publication was made possible through support provided to BSP by the Global Bureau of USAID, under the terms of Cooperative Agreement Number DHR-A-00-88-00044-00. The opinions expressed herein are those of the authors and do not necessarily reflect the views of USAID.